A structure optimization method of a dual-axis excitation phase modifier

Abstract

The application relates to the technical field of motor structure, and particularly discloses a structure optimization method of a double-shaft excitation phase modifier, which comprises the following steps: S1, determining a magnetic motive force according to a kth harmonic magnetic motive force of a double-layer short-distance coil of the double-shaft excitation phase modifier; S2, respectively merging the magnetic motive forces under different working conditions to obtain a resultant magnetic motive force; S3, determining a rotor pitch according to an excitation mode of a motor of the double-shaft excitation phase modifier; the excitation mode comprises direct-current excitation and alternating-current excitation; S4, taking the minimum of the excitation current under three-phase short-circuit and variable-speed operation as an optimization target, and determining a slot wedge conductivity; and S5, determining the structure of the double-shaft excitation phase modifier according to the resultant magnetic motive force, the rotor pitch and the slot wedge conductivity. The application can provide inertia support for a system and inhibit frequency fluctuation.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of motor structures, in particular to a structure optimization method of a double-shaft excitation phase modifier. BACKGROUND

[0002] With the continuous development, new energy mainly including photovoltaic power and wind power gradually becomes the main body of power supply. Considering the characteristics of low inertia and weak anti-interference of power electronic devices, with the increasing penetration of power electronics, the current new power system has problems such as insufficient system inertia and frequency modulation capacity and low frequency stability level.

[0003] The double-shaft alternating current excitation phase modifier provides valuable inertia support for the power system through the mechanical inertia of the rotating rotor. When the system frequency fluctuates due to power imbalance, the large moment of inertia of the rotor can instantaneously absorb or release kinetic energy, resist the mutation rate of frequency, and slow down the falling or rising speed of frequency. This inertia response gains critical time for the system, so that other standby power sources can start and intervene in regulation to compensate for the power difference, thereby significantly enhancing the frequency stability of the system and effectively suppressing the rapid fluctuation of the system frequency, which is crucial to maintaining the safe and stable operation of the power grid.

[0004] Among them, the structure of the motor has a decisive influence on its key performance indicators. The total mass, diameter and length ratio and material density of the rotor directly determine its moment of inertia. Greater moment of inertia means that more kinetic energy can be stored when the system is disturbed, providing stronger inertia support. The lamination material of the stator and rotor core, the magnetic circuit length and the air gap size directly affect the size and efficiency of the excitation current required to establish the magnetic field. Small air gap means small magnetic resistance and high excitation efficiency, but the manufacturing and operation requirements are more stringent. Core material, lamination thickness, magnetic flux density design and slot structure design are the main determinants of iron loss. High-frequency harmonics increase iron loss. Therefore, it is necessary to optimize the structure of the motor. SUMMARY

[0005] In view of the above problems, the purpose of the application is to provide a structure optimization method of a double-shaft excitation phase modifier, which can provide inertia support for the system and suppress frequency fluctuations.

[0006] The application provides a structure optimization method of a double-shaft excitation phase modifier, comprising:

[0007] Step S1, determining the magnetic motive force according to the kth harmonic magnetic motive force of the double-layer short-pitch coil of the double-shaft excitation phase modifier;

[0008] Step S2, merging the magnetic motive forces of different working conditions respectively to obtain a synthesized magnetic motive force;

[0009] Step S3, determining the rotor pitch according to the excitation mode of the motor of the double-shaft excitation phase modifier; the excitation mode includes direct current excitation and alternating current excitation.

[0010] Step S4, the slot wedge conductivity is determined with the minimum excitation current in three-phase short-circuit and variable-speed operation as the optimization target;

[0011] Step S5, the structure of the two-shaft excitation phase modifier is determined according to the synthesized magnetomotive force, the rotor pitch and the slot wedge conductivity.

[0012] In a possible implementation, the step S2 comprises:

[0013] When the motor is in synchronous operation and k = 1, 5, 9, 13…, the synthesized magnetomotive force is represented by the following formula :

[0014] ;

[0015] In the formula, is the magnetomotive force harmonic number, is the number of turns in series per phase, is the short pitch coefficient of k times, is the distribution coefficient of k times, is the number of slots per phase per pole, is the effective value of the excitation current, is the spatial angle of the phase modifier, is the synchronous angular velocity, is the time.

[0016] In a possible implementation, the step S2 further comprises:

[0017] When the motor is in synchronous operation and k = 3, 7, 11, 15…, the synthesized magnetomotive force is represented by the following formula :

[0018] ;

[0019] In the formula, is the magnetomotive force harmonic number, is the number of turns in series per phase, is the short pitch coefficient of k times, is the distribution coefficient of k times, is the number of slots per phase per pole, is the effective value of the excitation current, is the spatial angle of the phase modifier, is the synchronous angular velocity, is the time.

[0020] In a possible implementation, the step S2 further comprises:

[0021] When the motor is in asynchronous operation and k = 1, 5, 9, 13…, the synthesized magnetomotive force is represented by the following formula :

[0022] ;

[0023] wherein, is the magnetic motive force harmonic order, is the number of series turns per phase, is the short pitch coefficient of kth order, is the distribution coefficient of kth order, is the effective value of field current, is the number of slots per pole per phase, is the spatial angle of the phase modifier, is the synchronous angular velocity, is time, is the rotor electrical angular velocity.

[0024] In a possible implementation, the step S2 further comprises:

[0025] When the motor is operated asynchronously and k = 3, 7, 11, 15, …, the resultant magnetic motive force is represented according to the following formula :

[0026] ;

[0027] wherein, is the magnetic motive force harmonic order, is the number of series turns per phase, is the short pitch coefficient of kth order, is the distribution coefficient of kth order, is the effective value of field current, is the number of slots per pole per phase, is the spatial angle of the phase modifier, is the synchronous angular velocity, is time, is the rotor electrical angular velocity.

[0028] In a possible implementation, it further comprises:

[0029] The d-axis current and the q-axis current are represented according to the following formula :

[0030] ;

[0031] wherein, is the synchronous angular velocity, is the rotor electrical angular velocity, is time, is the effective value of field current.

[0032] In a possible implementation, the step S3 comprises:

[0033] When the excitation mode of the motor is DC excitation, the rotor pitch is determined as 5 / 6 pitch or 2 / 3 pitch.

[0034] In a possible implementation, the step S3 further comprises:

[0035] When the excitation mode of the motor is AC excitation, the rotor pitch is determined as 5 / 6 pitch.

[0036] In a possible implementation, the step S4 comprises:

[0037] The transient index representing the excitation current size is determined as an optimization target of the minimum excitation current when the motor is in three-phase short circuit and variable speed operation;

[0038] The conductivity corresponding to the transient index is determined as the slot wedge conductivity.

[0039] In a possible implementation, the step S4 further comprises:

[0040] The transient index is represented according to the following formula :

[0041] ;

[0042] In the formula, is an inertia support coefficient, is a voltage support coefficient, is a variable speed operation excitation current reference value, is a short circuit fault excitation current reference value, is a variable speed operation excitation current, is a short circuit fault excitation current.

[0043] The structure optimization method of the dual-shaft excitation phase modifier provided by the application can provide inertia support for the system, suppress frequency fluctuation, effectively store energy for the motor, and has a decisive influence on excitation characteristics, loss, etc. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The flowchart of the structure optimization method provided by the embodiment of the application is shown. DETAILED DESCRIPTION

[0045] The embodiments of the application will be further described in detail below with reference to the drawings and embodiments. The detailed description of the following embodiments and the drawings are used to exemplarily illustrate the principles of the application, but cannot be used to limit the scope of the application, that is, the application is not limited to the described preferred embodiments, and the scope of the application is defined by the claims.

[0046] In the description of this invention, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance; those skilled in the art can understand the specific meaning of the above terms in this invention as appropriate.

[0047] Figure 1 A flowchart illustrating the structural optimization method provided in an embodiment of the present invention is shown below. Figure 1 As shown, the present invention provides a structural optimization method for a dual-axis excitation camera, comprising:

[0048] Step S1: Determine the magnetomotive force based on the k-th harmonic magnetomotive force of the double-layer short-pitch coil of the dual-axis excitation phase modulator.

[0049] Step S2: Combine the magnetomotive forces under different operating conditions to obtain the composite magnetomotive force;

[0050] In one possible implementation, when the motors are running synchronously, the present invention assumes... = = .

[0051] When the motors are running synchronously and k = 1, 5, 9, 13…, the resulting magnetomotive force can be expressed by the following formula. :

[0052] ;

[0053] In the formula, For the harmonic order of magnetomotive force, Number of turns in series per phase For the short distance coefficient of order k, The distribution coefficient of the kth order, Number of slots per pole per phase The effective value of the excitation current, To adjust the camera's spatial angle, For synchronous angular velocity, For time.

[0054] When the motors are running synchronously and k = 3, 7, 11, 15, ..., the resulting magnetomotive force can be expressed by the following formula. :

[0055] ;

[0056] In the formula, For the harmonic order of magnetomotive force, Number of turns in series per phase For the short distance coefficient of order k, The distribution coefficient of the kth order, Number of slots per pole per phase The effective value of the excitation current, To adjust the camera's spatial angle, For synchronous angular velocity, For time.

[0057] When the motor is running asynchronously, this invention expresses the d-axis current according to the following formula. and q-axis current :

[0058] ;

[0059] In the formula, For synchronous angular velocity, For rotor electric angular velocity, For time, This is the effective value of the excitation current.

[0060] When the motor operates asynchronously and k = 1, 5, 9, 13…, the resulting magnetomotive force is expressed by the following formula. :

[0061] ;

[0062] In the formula, For the harmonic order of magnetomotive force, Number of turns in series per phase For the short distance coefficient of order k, The distribution coefficient of the kth order, The effective value of the excitation current, Number of slots per pole per phase To adjust the camera's spatial angle, For synchronous angular velocity, For time, ω is the rotor's electric angular velocity.

[0063] In one possible implementation, step S2 further includes:

[0064] When the motor operates asynchronously and k=3,7,11,15,…, the resulting magnetomotive force is expressed by the following formula. :

[0065] ;

[0066] In the formula, For the harmonic order of magnetomotive force, Number of turns in series per phase For the short distance coefficient of order k, The distribution coefficient of the kth order, The effective value of the excitation current, for each pole and each phase slot number, for the spatial angle of the phase modifier, for the synchronous angular velocity, for the time, for the rotor electrical angular velocity.

[0067] The harmonic magnetic motive force rotation speed is expressed as wherein, for the rotor electrical angular velocity, for the synchronous angular velocity.

[0068] Step S3, determining the rotor pitch according to the excitation mode of the motor of the two-axis excitation phase modifier; the excitation mode includes direct current excitation and alternating current excitation;

[0069] In a possible implementation, when the excitation mode of the motor is direct current excitation, the rotor pitch is determined as 5 / 6 rotor pitch or 2 / 3 rotor pitch. When the excitation mode of the motor is alternating current excitation, the rotor pitch is determined as 5 / 6 rotor pitch.

[0070] Specifically, the two-axis excitation motor structure uses a two-phase winding. According to the magnetic motive force expression, when the excitation frequency is 5 Hz, the 3rd harmonic magnetic motive force causes the stator electromotive force to have a 130 Hz frequency component. When the rotor pitch is 5 / 6, the stator electromotive force has a large 130 Hz frequency component, verifying that the stator electromotive force amplitude fluctuation is derived from the 3rd harmonic magnetic motive force. In order to optimize the rotor pitch, the stator electromotive force waveforms of the 5 / 6 rotor pitch and the 2 / 3 rotor pitch are calculated by finite element method with and without damping. The results show that: when the motor is excited by direct current, the stator electromotive force waveforms of the two pitches are good; while when excited by alternating current, the stator electromotive force of the 5 / 6 pitch has obvious amplitude fluctuation, and the damping will exacerbate this amplitude fluctuation. While the 2 / 3 pitch stator electromotive force amplitude fluctuation is significantly weakened.

[0071] Step S4, determining the slot wedge conductivity with the minimum excitation current of three-phase short-circuit and variable-speed operation as the optimization target;

[0072] In a possible implementation, the transient index representing the excitation current is determined with the minimum excitation current of three-phase short-circuit and variable-speed operation as the optimization target; the conductivity corresponding to the transient index is the slot wedge conductivity.

[0073] Specifically, in order to further study the influence of the slot wedge conductivity on the inertia support and the transient characteristics of the fault working condition, the excitation current when the speed is 0.9 p.u. and the maximum excitation current when the three-phase short circuit occurs are calculated under the inertia support of different conductivities. With the increase of the slot wedge conductivity, the excitation current gradually decreases when the short circuit fault occurs, and the excitation current gradually increases when the variable speed operation occurs. In order to optimize the conductivity of the damping winding, the transient index F is proposed to characterize the excitation current of the double-shaft excitation phase modifier when the three-phase short circuit and the variable speed operation occur, and the excitation current is minimized as the optimization objective.

[0074] In a possible implementation, the transient index F is expressed according to the following formula :

[0075] ;

[0076] In the formula, I is the inertia support coefficient, is the voltage support coefficient, is the variable speed operation excitation current reference value, is the short circuit fault excitation current reference value, is the variable speed operation excitation current, is the short circuit fault excitation current.

[0077] wherein 0 <1, =1- . The size of F can be selected according to different requirements for transient voltage and inertia support. The smaller F is, the greater the weight of the transient voltage support is; The greater F is, the greater the weight of the inertia support is. In particular, F = 0.5 indicates that the weights of the transient voltage and the inertia support are the same.

[0078] In step S5, the structure of the double-shaft excitation phase modifier is determined according to the synthesized magnetomotive force, the rotor pitch and the slot wedge conductivity.

[0079] In an example, the 10.5 kV 50 Mvar double-shaft excitation phase modifier is designed by using the electromagnetic design software in the application example.

[0080] The current, the magnetic flux density and the loss characteristics of the motor in the three working conditions of no-load, synchronous operation and asynchronous operation to output 50 Mvar are calculated. The current and the magnetic flux density characteristics of different working conditions are shown in Table 1. The loss characteristics under different working conditions are shown in Table 2.

[0081] Table 1

[0082] ​​​

[0083] Table 2

[0084]

[0085] It can be seen that the no-load excitation current of the motor is 931 A, and the excitation current when generating 50 Mvar reactive power is 2927 A. The maximum stator flux density is 1.76 T, the maximum rotor flux density is 1.04 T, the maximum stator current density is 3.2 A / mm 2 , and the maximum rotor current density is 4 A / mm 2 , all of which do not exceed the limit value that the motor material can withstand. At the same time, the motor efficiency reaches more than 96%. Therefore, the motor design scheme is very reasonable.

[0086] The current, flux density and loss characteristics of the motor under three working conditions of no-load, synchronous operation generating 50 Mvar, and asynchronous operation generating 50 Mvar are calculated by using the finite element method. In the no-load working condition, the d-axis and q-axis excitation currents I fd = I fq = 790 A, the speed n = 1500 rpm, and the key indicators of the no-load working condition are shown in Table 3.

[0087] Table 3

[0088]

[0089] In the synchronous operation generating 50 Mvar reactive power, the excitation current effective value is 2895 A, the speed n = 1500 rpm, and the key indicators of the synchronous operation working condition are shown in Table 4.

[0090] Table 4

[0091]

[0092] In the asynchronous operation generating 50 Mvar reactive power, the excitation current effective value is 2895 A, the speed n = 1350 rpm, and the key indicators of the asynchronous operation working condition are shown in Table 5.

[0093] Table 5

[0094]

[0095] It can be seen that the calculation results are not much different from the results of the electromagnetic design software, further verifying the accuracy of the electromagnetic design software.

[0096] The application provides a structure optimization method of a double-shaft excitation phase modifier, which comprises the following steps: firstly, determining the diameter and the core length of the stator and the rotor; then, selecting a proper slot wedge material; then, judging whether the excitation current at the rotor speed of 0.9p.u. and the maximum excitation current at three-phase short circuit are within the required range; if not, reselecting the slot wedge conductivity and then deducing the rotor magnetomotive force; if yes, then calculating the rotor magnetomotive force; if the rotor magnetomotive force does not meet the requirement, re-determining the above-mentioned content; and if the requirement is met, optimizing the pitch of the rotor to reduce the harmonic magnetomotive force. The application can provide inertia support for the system, suppress frequency fluctuation, effectively store energy for the motor, and has a decisive influence on excitation characteristics, loss and the like.

[0097] The above merely describes the specific implementation of the application, but the protection scope of the application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the application, which should be covered by the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A method for structural optimization of a two-axis field-oriented machine, characterized in that, The method comprises the following steps: Step S1, determining the magnetomotive force according to the k-th harmonic magnetomotive force of the double-layer short-pitch coil of the double-shaft excitation phase modifier; Step S2, combining the magnetomotive forces of different working conditions respectively to obtain a resultant magnetomotive force; Step S3, determining the rotor pitch according to the excitation mode of the motor of the double-shaft excitation phase modifier; the excitation mode comprises direct current excitation and alternating current excitation; Step S4, determining the slot wedge conductivity with the minimum excitation current in three-phase short-circuit and variable-speed operation as the optimization target; Step S5, determining the structure of the double-shaft excitation phase modifier according to the resultant magnetomotive force, the rotor pitch and the slot wedge conductivity; The step S4 comprises: determining a transient index representing the excitation current with the minimum excitation current in three-phase short-circuit and variable-speed operation as the optimization target; and determining the conductivity corresponding to the transient index as the slot wedge conductivity; The transient indicator is expressed according to the following formula : In the formula, is an inertia support coefficient, is a voltage support coefficient, is a variable speed operation excitation current reference value, is a short circuit fault excitation current reference value, is a variable speed operation excitation current, is a short circuit fault excitation current.

2. The method for structural optimization of claim 1, wherein, The step S2 comprises: When the motor is running synchronously and k = 1, 5, 9, 13..., the resultant magnetomotive force is expressed according to the following formula : wherein is the magnetic motive force harmonic number, is the number of series turns per phase, is the short pitch factor of the kth harmonic, is the distribution factor of the kth harmonic, is the number of slots per pole per phase, is the effective value of the field current, is the space angle of the phase modifier, is the synchronous angular velocity, is the time.

3. The method of structural optimization according to claim 2, characterized in that, The step S2 further comprises: When the motor is running synchronously and k = 3, 7, 11, 15,..., the resultant magnetomotive force is expressed according to the following formula : wherein is the magnetic motive force harmonic number, is the number of series turns per phase, is the short pitch factor of the kth harmonic, is the distribution factor of the kth harmonic, is the number of slots per pole per phase, is the effective value of the field current, is the space angle of the phase modifier, is the synchronous angular velocity, is the time.

4. The method for structural optimization of claim 1, wherein, The step S2 further comprises: When the motor is operated asynchronously and k = 1, 5, 9, 13..., the resultant magnetomotive force is expressed according to the following equation : wherein is the magnetic motive force harmonic number, is the number of series turns per phase, is the short pitch factor of kth order, is the distribution factor of kth order, is the effective value of the field current, is the number of slots per pole per phase, is the space angle of the phase modifier, is the synchronous angular velocity, is the time, is the rotor electrical angular velocity.

5. The method of structural optimization according to claim 4, characterized in that, The step S2 further comprises: When the motor is operated asynchronously and k = 3, 7, 11, 15,..., the resultant magnetomotive force is expressed according to the following equation : wherein is the magnetic motive force harmonic number, is the number of series turns per phase, is the short pitch factor of kth order, is the distribution factor of kth order, is the effective value of the field current, is the number of slots per pole per phase, is the space angle of the phase modifier, is the synchronous angular velocity, is the time, is the rotor electrical angular velocity.

6. The method for structural optimization of claim 4, wherein, The step S2 further comprises: The d-axis current is expressed according to the following equation and the q-axis current : wherein is the synchronous angular velocity, is the rotor electric angular velocity, is the time, is the field current effective value.

7. The method for structural optimization of claim 1, wherein, The method further comprises: The step S3 comprises:

8. The method of structural optimization according to claim 7, characterized in that, When the excitation mode of the motor is direct current excitation, the rotor pitch is determined as the rotor 5 / 6 pitch or the rotor 2 / 3 pitch. The step S3 further comprises: When the excitation mode of the motor is alternating current excitation, the rotor pitch is determined as the rotor 5 / 6 pitch.

Images